1. Field of the Invention
The present invention relates to on-board cab signaling systems and, more particularly, to the rejection of magnetic field interference imposed on inductive track receivers employed by these systems.
2. Description of the Prior Art
Cab signals are utilized extensively to communicate information to a cab signal system located on-board a locomotive. This information is utilized by the cab signal system to provide information to an operator of a locomotive or to automatically control the operation of the locomotive.
Cab signal systems typically employ inductive track receivers mounted on the locomotive ahead of the lead wheels and just above the rails for sensing and converting magnetic fields produced by cab signal carriers transmitted through the rails into cab signals. An advantage of cab signals is that information can be made available to the locomotive operator on a continuous basis. This is especially useful for communicating instantaneous changes in the status of a track circuit to operators of locomotives on the track circuit. By communicating this information on a continuous basis, locomotives can be controlled to safely proceed through the track circuit.
A prior art track receiver typically includes an iron core inductor mounted above and orthogonal to a longitudinal axis of a rail. The frequency of the cab signal carrier transmitted through the rails is typically in the range from 40 Hz to 250 Hz, but may be as high as 5 kHz. Prior art track receivers are utilized quite successfully in older model locomotives which utilize DC traction motors. Modern locomotives, however, utilize AC traction motors which receive alternating current power from an inverter. The combination of an AC traction motor and inverter provides a greater degree of speed, power and control over a DC traction motor while eliminating the high maintenance requirements associated with the use of DC traction motors.
An AC traction motor receives alternating current from the inverter at a variable frequency between 0 Hz and 300 Hz according to the speed requirement of the train. This results in the generation of an alternating current magnetic field by the AC traction motor that did not exist with DC traction motors. Since the frequency of the alternating current magnetic field generated by the AC traction motor is in the same frequency range as cab signal carriers, the AC traction motor is a primary source of noise signals which can be imposed on the track receivers along with the cab signals. Thus, the use of AC traction motors can severely compromise cab signals as a safe and reliable information source.
Various approaches for reducing the effect of the alternating current magnetic fields and, hence, noise signals produced by an AC traction motor have been proposed. One approach is disclosed in U.S. Pat. No. 5,586,736 to Mollet. The Mollet patent discloses pickup units 44 each having a housing 48 with a rectangular configuration but for a missing lower side thus forming an inverted, hollow U-shaped enclosure. An inverted U-shaped magnetic structure is received in housing 48 and is essentially centered within top and end segments 50 and 52 of housing 48. The magnetic structure includes a pair of vertical legs 54 and a horizontal cross member 56. Legs 54 and cross member 56 are formed from cylindrical ferrite rods. Each pickup unit 44 is positioned and oriented so that legs 54 extend toward the rail thereby enhancing the capacity of each pickup unit 44 to receive magnetic fields produced by the cab signal carriers. A pickup coil 58 or 60 is wound on each leg 54. Pickup coils 58 and 60 are connected so that cab signals produced by coils 58 and 60 are additive and noise signals produced by coils 58 and 60 are subtractive.
Another approach proposed in U.S. Pat. No. 5,622,339 to Capan is a pair of plate antennas for sensing the magnetic fields produced by the cab signal carrier. Each plate antenna includes a signal coil and a noise coil wound on a rectangular core at right angles to each other. The signal coils and the noise coils of the plate antennas are connected so that the outputs of the noise coils cancel any noise components in the signals output by the signal coils, such as noise components caused by the operation of the AC traction motor.
As can be seen from the Mollet and Capan patents, those skilled in the art of cab signaling systems believed it necessary for each track receiver to maintain an orthogonal relationship with the rail, to modify the shape of the track receiver, to utilize high permeability materials and/or to utilize additional windings to subtract out motor noise from the cab signal. These solutions, however, are specialized and/or costly and require application specific tuning and calibration by empirical testing. In addition, these solutions have limited capacity to completely subtract out motor noise due to mutual coupling of the signal and noise coils.
It is, therefore, an object of the present invention to overcome the above problem and others by providing a cab signaling system having an track receiver oriented to minimize the effects of magnetic field motor noise produced by a traction motor during operation while, at the same time, detecting magnetic fields produced by a cab signal carriers transmitted through the rails with an acceptable signal to noise ratio. Still other objects of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.
Accordingly, I have invented a system for use on a locomotive having a traction motor which generates a first magnetic field during operation. The system includes at least one track receiver located on-board the locomotive and disposed in a second magnetic field produced around at least one of a pair of rails on which the locomotive is carried in response to a cab signal carrier propagating through the at least one rail. The track receiver converts the second magnetic field into a cab signal. The track receiver is also disposed in the first magnetic field generated during operation of the traction motor of the locomotive for converting the first magnetic field into a noise signal. A cab signal system located on-board the locomotive is connected to receive the cab signal and the noise signal from the track receiver. The cab signal system is configured to extract data from the cab signal which has a frequency range at least partially in common with a frequency range of the noise signal. The first magnetic field propagates in a three dimensional space around the traction motor. The first magnetic field has at each point in the three dimensional space a magnetic vector which, with reference to a Cartesian coordinate system, is comprised of a horizontal component which extends parallel to the longitudinal axes of the rails adjacent the locomotive, a lateral component which extends laterally to the longitudinal axes of the rails adjacent the locomotive and a vertical component which extends perpendicular to the horizontal and lateral components. The track receiver is positioned on the locomotive in the three dimensional space and is oriented so that at the points in the three dimensional space where the track receiver is positioned the vector sum of at least two of the horizontal, lateral and vertical components has a direction vector substantially perpendicular to an axis of sensitivity of the track receiver where the track receiver is most sensitive to a magnetic field propagating therealong.
The track receiver is positioned on the locomotive so that a magnetic vector of the second magnetic field produced around the at least one rail propagates through the track receiver substantially parallel to the axis of sensitivity of the track receiver.
The axis of the sensitivity of the track receiver can be received in an imaginary plane which extends substantially parallel to top surfaces of the rails. The traction motor has a longitudinal axis which extends transverse to the longitudinal axes of the rails. The track receiver is positioned adjacent one of the rails and, when viewed normal to a surface of the imaginary plane, an extension of the axis of sensitivity of the track receiver crosses an extension of the longitudinal axis of the traction motor on a side of the one rail opposite the other rail. Preferably, the longitudinal axis of the traction motor extends laterally to the longitudinal axes of the rails.
When the track receiver is positioned on the locomotive and oriented so that the vector sum of two of the vertical, horizontal and lateral components, at the points in the three dimensional space where the track receiver is positioned, has a direction vector substantially perpendicular to the axis of sensitivity of the track receiver, the remaining one of the vertical, horizontal and lateral components has a direction vector substantially perpendicular to the axis of sensitivity of the track receiver.
At least one of the vertical, horizontal and lateral components can have a magnitude of zero. Preferably, the track receiver is comprised of (i) a coil of wire or (ii) a Hall-effect sensor.
Alternatively, the axis of sensitivity of the track receiver can be received in an imaginary plane which extends laterally and substantially perpendicular to the longitudinal axes of the rails. Where the traction motor has a longitudinal axis which extends transverse to the longitudinal axes of the rails and the track receiver is positioned adjacent one of the rails, when viewed normal to a surface of the imaginary plane, an extension of the axis of sensitivity of the track receiver crosses an extension of the longitudinal axis of the traction motor on a side of the one rail opposite the other rail.
I have also invented a system for use on a rail vehicle received on a pair of rails and having a traction motor which generates a magnetic field which propagates in a three dimensional space around the traction motor. The magnetic field has at each point in the three dimensional space a magnetic vector which, with reference to a Cartesian coordinate system in the three dimensional space, is comprised of the vector sum of three components which extend perpendicular to each other with one of the three perpendicular components parallel to the longitudinal axes of the rails. The system includes a track receiver positioned on-board the rail vehicle in the three dimensional space adjacent one of the rails and oriented in the three dimensional space so that at the points in the three dimensional space where the track receiver is positioned the vector sum of at least two of the three perpendicular components has a direction vector substantially perpendicular to an axis of sensitivity of the track receiver.
The system can also include another track receiver positioned on-board the rail vehicle in the three dimensional space adjacent the other rail and oriented in the three dimensional space so that at the points in the three dimensional space where the other track receiver is positioned the vector sum of at least two of the three perpendicular components has a direction vector substantially perpendicular to an axis of sensitivity of the other track receiver.
Preferably, the axis of sensitivity of each track receiver is positioned at a compound angle comprising a first angle relative to a first plane which extends parallel to top surfaces of the rails and a second angle relative to a second plane which extends laterally and perpendicular to the longitudinal axes of the rails.
The track receivers are preferably connected so that cab signals output by the track receivers in response to a cab signal carrier flowing through the rail adjacent each track receiver are additive.
Each track receiver is also oriented relative to its adjacent rail so that a magnetic vector of another magnetic field produced around the rail in response to the cab signal carrier flowing therethrough propagates through the track receiver substantially parallel to the axis of sensitivity of the track receiver.
Lastly, I have invented a cab signaling system for use on a locomotive having a traction motor positioned between a front end and a back end of the locomotive. The system includes a first track receiver disposed on-board the locomotive adjacent one of a plurality of rails which support the locomotive and in a magnetic field generated by the traction motor during operation. The first track receiver outputs a first cab signal in response to a cab signal carrier transmitted through the rail adjacent the first track receiver. The first track receiver also outputs in response to the magnetic field a first signal noise having a frequency in a frequency range of the first cab signal. The first track receiver has an axis of sensitivity which is oriented at a first position in the magnetic field substantially perpendicular to a direction vector of the magnetic field at the first position. A signal processor located on-board the locomotive is connected to receive from the first track receiver the first cab signal and the first noise signal. The signal processor is configured to process signals in the frequency range of the first cab signal. The orientation of the axis of sensitivity of the first track receiver in the magnetic field results in a ratio of the first cab signal to the first noise signal being of a sufficient extent so that the signal processor can process the first cab signal without interference by the first noise signal.
The system can also include a second track receiver disposed on-board the locomotive adjacent another one of the plurality of rails and in the magnetic field. The second track receiver outputs a second cab signal in response to transmission of the cab signal carrier through the rail adjacent the second track receiver. The second track receiver also outputs in response to the magnetic field a second noise signal having a frequency in a frequency range of the second cab signal. The second track receiver has an axis of sensitivity which is oriented at a second position in the magnetic field substantially perpendicular to a direction vector of the magnetic field at the second position. The signal processor is connected to receive from the second track receiver the second cab signal and the second noise signal and to process signals in the frequency range of the second cab signal. The orientation of the axis of sensitivity of the second track receiver in the magnetic field results in a ratio of the second cab signal to the second noise signal being of a sufficient extent so that the signal processor can process the second cab signal without interference by the second noise signal.
Preferably, the first and second track receivers are connected so that the first and second cab signals sum and the first and second noise signals sum. The orientation of the axes of sensitivity of the first and second track receivers in the magnetic field results in a ratio of the sum of the cab signals to the sum of the noise signals being of a sufficient extent so that the signal processor can process the sum of the cab signals without interference from the sum of the noise signals.